The Contarex Lens to Sony NEX Camera Speed Booster from Metabones allows a full frame Contarex lens to be mounted to an NEX APS-C format camera and in doing so, increases the angle of view and increases the maximum aperture one f/stop.
When a lens intended for full frame sensors or 35mm film is mounted to a camera with an APS-C sized sensor, it transmits a larger area of light than the smaller sensor was built to accept and therefore the effective angle of view of the lens increases. The Speed Booster condenses light from the lens and projects it onto the APS-C sensor allowing the sensor to utilize all of the lens' light and effectively produce a full-frame angle of view with an APS-C sensor. A corresponding increase in the maximum aperture of one f/stop makes the lens more effective in low-light situations and able to create a shallow depth of field.
Metabones Speed Boosters are quality made, using precision-machined brass with chromium plating on both the camera body and the lens side of the booster in order to ensure smooth mounting, quality aesthetic, and durability. This adapter has a detachable tripod foot that is compatible with Arca Swiss, Markins, and Photo Clam ball heads.
Although the lens will fit physically, automatic diaphragm (AE metering), or other auto functions are not retained using this speed booster. This adapter provides a built-in aperture control ring.
These speed boosters are only fully compatible with mirrorless cameras housing APS-C or smaller image sensors. They will physically fit the Sony A7/A7R full frame mirrorless cameras but the camera must be set in Crop Mode to fully support the speed booster's functions.